1. Field of the Invention
The present invention generally relates to a development device, an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine having at least two of these capabilities, that includes a development device, and a process unit that includes a development device and incorporated in an image forming apparatus.
2. Description of the Related Art
There are development devices that include, as a developer bearer, a development roller having a surface roughened by sandblasting or the like to help toner carried thereon to follow the movement of the development roller, thereby facilitating conveyance of toner. In configurations in which the surface of the development roller is roughened, the thickness of a thin toner layer formed on the development roller is kept uniform to equalize the amount of toner transported to a development range where the development roller faces a latent image bearer such as a photoreceptor. Typically, a developer regulator such as a doctor blade is disposed in contact with the development roller at the entrance of the development range to adjust the thickness of the toner layer.
For example, JP-2009-109558-A proposes forming multiple recesses in the surface of the development roller and leveling off toner carried on the development roller using a developer regulator in contact with the surface of the development roller. Specifically, while toner is kept in the recesses, the developer regulator scrapes off toner present higher than the upper end of the recess from the development roller. With this configuration, the amount of toner transported to the development range is similar to the capacity of the recesses, thereby keeping the amount of toner transported uniform. Additionally, only toner inside the recesses passes under the developer regulator, and a strong pressure is not applied to the toner passing by the developer regulator. Accordingly, filming of toner can be inhibited.
In this configuration, an insulative layer formed of the insulative toner is formed on the surface of the development roller downstream from the contact area with the regulation blade, aiming at inhibiting electrical discharge between a solid surface in the areas not recessed (hereinafter “reference surface area”) of the development roller and the photoreceptor.
Specifically, the insulative toner adhering to the reference surface area of the development roller is removed by the regulation blade at the entrance of the contact area between the development roller and the regulation blade. In the contact area therebetween, the insulative toner is retained inside the recesses closed by the regulation blade being contact with the development roller. Among insulative toner particles retained in the recesses, toner particles directly contacting the inner wall of the recess is strongly adsorbed to the inner wall of the recess by the force of mirror image. By contrast, toner particles not in direct contact with the inner wall of the recess are subject to a weaker adsorption force. In this state, when the regulation blade closing the recess leaves the development roller at the exit of the contact area between the development roller and the regulation blade, toner particles not in direct contact with the inner wall of the recess are electrostatically attracted to the solid surface in the reference surface area of the development roller and transferred thereto. Thus, a layer of insulative toner is formed on the development roller downstream from the regulation blade.